Conventional so-called atmospheric crude distillation units used for separating the desirable components of crude oil typically have an atmospheric crude tower, a naphtha splitter or naphtha stripper to separate the straight run naphtha into light straight run (LSR) naphtha and heavy naphtha, and several side strippers to produce components such as diesel, kerosene, and atmospheric gas oil. Traditionally, such atmospheric crude distillation units operate at near atmospheric pressure in order to evaporate all desirable components without exceeding cracking temperatures in the bottom of the crude distillation tower. This has led to the auxiliaries around the crude distillation tower being operated at about the same pressure as well.
In units of this type, the overhead product of the atmospheric crude tower either is a full range naphtha which is subsequently split into an LSR naphtha and a heavy straight run naphtha in a naphtha splitter, or the LSR naphtha is recovered as an overhead product of the atmospheric crude tower and the heavy naphtha is produced as the bottom product of a naphtha side-stripper connected to the atmospheric crude tower.
In both types of operation described above, low temperatures in the top section of the atmospheric crude tower may result in water condensation on the upper trays. This condensed water can be very corrosive because the separated water will typically contain H.sub.2 S and other sulfur compounds obtained from the crude oil. Hence, special metallurgy is required for the tower internals such as linings and trays and the overhead condensing system. In addition, special tray types have to be used for withdrawing water from the trays, and in the presence of water the fractionation efficiency of the tower may decrease as well.
Previously known crude separation systems may include a preflash tower upstream of the atmospheric crude tower removing most of the not readily condensible components present in the crude oil charge, thereby reducing the load on the atmospheric crude tower. Such preflash towers typically operate at pressure of less than 25 psig.
Since all of these prior art methods operate at a relatively low pressure, any off-gases collected from the overhead system have to be compressed, since refinery fuel gas systems generally operate at a much higher pressure (usually higher than 50 psig). Compressing any substantial amount of gas consumes a high amount of energy.
Accordingly, there exists a need for a crude oil component separation method that will separate not readily condensable components at a sufficiently high pressure to eliminate the need for an off-compressor and that will effectively and efficiently separate light and heavy naphtha components and other crude oil components while avoiding the problems of water condensation in the top of the distillation tower and the corrosion caused thereby.